Motherhood status and union formation in Moshi, Tanzania 2002-2003

Age at first union is increasing throughout much of sub-Saharan Africa at the same time that not all couples are waiting for marriage before their first sexual intercourse. We assessed the effect of a premarital first birth on entrance into a first union in an urban area in East Africa -- Moshi, Tanzania. The data come from the Moshi Infertility Survey of 2002-2003. Women who spent less than a year in single motherhood were significantly more likely than childless women to enter into a first union, although the magnitude of this relationship was weaker for more recent cohorts. Women who had been single mothers for 5 or more years (about two-thirds of women with a premarital birth) were significantly less likely than women without children to enter into a first union.     

Brief proofs of Arrovian impossibility theorems

Since Kenneth Arrow showed the general possibility theorem, a number of social choice theorists have provided alternative proofs of it. In a recent article, Geanakoplos (Econ Theory 26:211–215, 2005) has constructed a new proof of the theorem. The present article provides alternative proofs of various Arrovian impossibility results from the 1960s to the 1970s by utilizing Geanakoplos’s method. We prove semi-order impossibility theorems, the quasi-transitive veto theorem, the quasi-transitive dictatorship theorem, the triple acyclic veto theorem, and the impossibility theorem without the Pareto principle.     

Causes of Civil War in Asia and Sub‐Saharan Africa: A Comparison*

Objectives. This article explores the extent to which economic development, ethnic and religious fractionalization, domestic governance, and international trade openness affect civil war in postcolonial Asia and Sub‐Saharan Africa (SSA) from 1950 through 1992. Methods. We estimate a set of multivariate logit models with the generalized estimating equation (GEE) method for time‐series cross‐sectional (TSCS) data. Results. Both in Asia and in SSA, civil war is less likely with increased economic development and trade openness, while mixed autocratic‐democratic regimes raise the likelihood that states will experience civil war. Although neither ethnic nor religious fractionalization has any statistically significant effect on civil war in SSA, civil war in Asia is more likely with greater ethnic fractionalization. Conclusions. Despite cross‐regional variation in causes of civil war, economic development and trade openness seem to play a consistent role in reducing civil war.     

Regression Diagnostics of the Semiparametric Proportional Rate Model for Irregularly Spaced Repeated Measurements

Counting process techniques have been successfully introduced to semiparametric inference of repeated measurements. Cheng and Wei (2000 Cheng , S. C. , Wei , L. J. ( 2000 ). Inference for a semiparametric model with panel data . Biometrika 87 : 89 – 97 .[Crossref], [Web of Science ®] , [Google Scholar]) proposed a simple inference procedure for the semiparametric proportional rate model, which reduces to relative risk regression models for binary data. While the baseline mean functions are completely unspecified, it still requires several assumptions for valid inference. In this article, a goodness-of-fit test for it is proposed based on cumulative residuals. Theoretical justification is provided and an illustration with a dataset from a clinical trial is given. Results of simulation studies to evaluate finite sample performance are also provided.     

Estimation of treatment effects based on possibly misspecified Cox regression

In randomized clinical trials, a treatment effect on a time-to-event endpoint is often estimated by the Cox proportional hazards model. The maximum partial likelihood estimator does not make sense if the proportional hazard assumption is violated. Xu and O'Quigley (Biostatistics 1:423-439, 2000) proposed an estimating equation, which provides an interpretable estimator for the treatment effect under model misspecification. Namely it provides a consistent estimator for the log-hazard ratio among the treatment groups if the model is correctly specified, and it is interpreted as an average log-hazard ratio over time even if misspecified. However, the method requires the assumption that censoring is independent of treatment group, which is more restricted than that for the maximum partial likelihood estimator and is often violated in practice. In this paper, we propose an alternative estimating equation. Our method provides an estimator of the same property as that of Xu and O'Quigley under the usual assumption for the maximum partial likelihood estimation. We show that our estimator is consistent and asymptotically normal, and derive a consistent estimator of the asymptotic variance. If the proportional hazards assumption holds, the efficiency of the estimator can be improved by applying the covariate adjustment method based on the semiparametric theory proposed by Lu and Tsiatis (Biometrika 95:679-694, 2008).     

Mantel-Haenszel estimators for irregular sparse K2×J tables

This paper deals with sparse K2×J(J>2)$K2\times J(J>2)$ tables. Projection-method Mantel–Haenszel (MH) estimators of the common odds ratios have been proposed for K2×J$K2\times J$ tables, which include Greenland's generalized MH estimator as a special case. The method projects log-transformed MH estimators for all K2×2$K2\times 2$ subtables, which were called naive MH estimators, onto a linear space spanned by log odds ratios. However, for sparse tables it is often the case that naive MH estimators are unable to be computed. In this paper we introduce alternative naive MH estimators using a graph that represents K2×J$K2\times J$ tables, and apply the projection to these alternative estimators. The idea leads to infinitely many reasonable estimators and we propose a method to choose the optimal one by solving a quadratic optimization problem induced by the graph, where some graph-theoretic arguments play important roles to simplify the optimization problem. An illustration is given using data from a case–control study. A simulation study is also conducted, which indicates that the MH estimator tends to have a smaller mean squared error than the MH estimator previously suggested and the conditional maximum likelihood estimator for sparse tables.     

1765年洪大容的中国京师行与1764年朝鲜通信使

在朝鲜与清朝的文化交流史上,1765年洪大容的中国之行具有划时代的意义,它重启了两国知识分子的交流,推动了朝鲜学术文化的进步,尤其值得关注的是洪大容与中国知识分子之间展现了"天涯知己"般的深厚友情。除燕行使外,朝鲜还有一条通往日本江户的通信使路线,1764年元重举就曾以此身份出使日本。如果将同时代燕行使与通信使的记录叠合观察,可以看到中、日、韩三国各自学术、文化及精神的相位。此外,从洪、元与中、日知识分子的交往经历,可以发现18世纪中、日存在相似的"情"的世界,而朝鲜则无。日本"古学"与清朝考证学都将"情"置于积极主张的地位,这造成了中、日两国与信奉朱子学、宋学的朝鲜在精神世界上的差异。     

Social choice, the strong Pareto principle, and conditional decisiveness

This paper examines social choice theory with the strong Pareto principle. The notion of conditional decisiveness is introduced to clarify the underlying power structure behind strongly Paretian aggregation rules satisfying binary independence. We discuss the various degrees of social rationality: transitivity, semi-transitivity, the interval-order property, quasi-transitivity, and acyclicity.